1. Field of the Invention
The invention relates to a torsional vibration damper for installation in a drive train of an automobile.
2. Description of the Related Art
For damping torsional vibrations in the drive train of an automobile, German Utility Model 94 14 314 discloses a torsional vibration damper comprising three flywheel mass arrangements which are arranged so as to be rotatable both jointly and relative to one another about a common first axis of rotation and which are coupled to one another by a planetary gear for the transmission of torsional forces. Two of the three flywheel mass arrangements are coupled to one another in a torsionally elastic manner by a spring arrangement. The first flywheel mass arrangement has an external toothing and comprises a sun wheel. Planet wheels which are rotatably mounted about second axes of rotation offset axially parallel to the first axis of rotation on the second flywheel mass arrangement are in meshed engagement with the external toothing. The second flywheel mass arrangement acts as a planet wheel carrier. Furthermore, the planet wheels are also in meshed engagement with a ring gear formed by an internal toothing provided on the third flywheel mass arrangement.
In this torsional vibration damper, an input side of one of the three flywheel mass arrangements is fastened to the crankshaft of an internal combustion engine and an output side of another of the three flywheel mass arrangements carries a frictional surface of a friction clutch. When a change in the torque is transmitted from the input-side to the output-side, the two flywheel mass arrangements are rotatable relative to one another. Due to the torsionally elastic coupling of the input and output ones of the three flywheel mass arrangements, the torque fluctuation is damped and the torsional deflection of the input-side flywheel mass arrangement relative to the output-side flywheel mass arrangement assumes a value which is determined primarily by the torque to be transmitted and the spring force of the spring arrangement.
To operate the known torsional vibration damper, the first, second or third flywheel mass arrangement may selectively be used as the input-side flywheel mass and one of the two remaining flywheel mass arrangements as the output-side flywheel mass. Furthermore, the spring arrangement acts both between the input-side and the output-side flywheel mass arrangement and between the remaining third flywheel mass arrangement, also designated as an intermediate mass, and either the input-side flywheel mass or the output-side flywheel mass.
One disadvantage of the known torsional vibration damper is that, when a torque to be transmitted fluctuates only slightly around an average value, such as occurs when an automobile travels evenly at an essentially constant speed for relatively long periods of time, the relative rotary positions of the flywheel mass arrangements, coupled to one another via the planetary gear change over long periods of time. Although the amplitude of this change is low, it causes a constant back and forth movement around a middle position. The result of this slow back and forth motion is that, in each case, only individual teeth of the sun wheel, of the planet wheels and of the ring gear participate in transmitting the torques which are sometimes high. In comparison with other teeth of the planetary gear, therefore, these individual teeth undergo substantially increased wear which may lead to the destruction of individual teeth of the planetary gear and consequently limits the useful life of the vibration damper.